The present invention relates to gas storage devices, and more specifically, to low pressure gas storage devices used in conjunction with gas produced by wastewater treatment plants.
The most familiar form of separate gas storage consists of fixed-volume, high pressure steel gas spheres. Storage is achieved by compressing the gas from 6-8 inches of water column, to 50-100 psig. The gas is then regulated back to 6-8 inches of water column, for use. These high pressure storage spheres and associated compressors are very expensive and require considerable operational and maintenance expenditures.
The use of digester tanks utilizing anaerobic processes to treat wastewater sludge is well known and practiced in the art. During the anaerobic process, gases, typically methane and carbon dioxide, are given off and collected to be used either as fuel for heating the sludge mixture, or for commercial use by utilities.
Typical anaerobic digester tanks have a capacity for the storage of evolved gasses which is limited by the size of the tank and the construction of the tank cover. Many of the systems employ a floating gas holder positioned above the sludge which collects the gas and exerts a controlled downward pressurizing force on it. Floating gas holders have proved to be less than satisfactory due to their inherent problems of corrosion, freezing, tipping and leaking.
Attempts to replace floating gas holders have typically involved the construction of a rigid dome over the digester tank, and at least one membrane located beneath the dome for collecting and pressurizing the gas, as well as a center stack or gas well to provide an attachment point for the membrane and access to the interior of the tank for periodic maintenance. Digester covers of this type are expensive to produce, and often provide limited gas storage capacity. In addition, many plant operators find that the technical and economic factors associated with converting conventional digester covers to fixed cover-membrane type apparatus make such conversions impractical.
Thus, there is a need for a relatively low cost, low maintenance gas storage system which can be located practically anywhere gas needs to be stored and, especially, separately from a gas-generating operation, such as an anaerobic wastewater treatment tank. It is the object of the present invention to provide a separate gas storage system which satisfies the above-identified design objectives.